1. Technical Field
The present invention relates to lasers and, in particular, to packaging for laser assemblies. Still more particularly, the present invention provides a method and apparatus for packaging a laser and a monitor photo detector on a wafer level planar assembly.
2. Description of the Related Art
Fiber optics are used for short distance communications. A laser (Light Amplification by the Stimulated Emission of Radiation) is a device that creates a uniform and coherent light that is very different from an ordinary light bulb. Many lasers deliver light in an almost-perfectly parallel beam (collimated) that is very pure, approaching a single wavelength. Solid state lasers create ultra-high-speed, miniscule pulses traveling in optical fibers. Light traveling in an optical fiber is impervious to external interference, which is a problem with electrical pulses in copper wire.
An optical fiber is a thin glass strand designed for light transmission. A single hair-thin fiber is capable of transmitting trillions of bits per second. There are two primary types of fiber. Multimode fiber is very common for short distances and has a core diameter of from 50 to 100 microns. For intercity cabling and highest speed, singlemode fiber with a core diameter of less than 10 microns is used.
Two examples of solid-state lasers are the edge emitting laser and the vertical cavity surface emitting laser (VCSEL). VCSELs are fabricated in a chip and the laser is emitted from the surface of the chip. A VCSEL has a wavelength of about 850 mm. A VCSEL can only be used with multimode fibers. Therefore, VCSELs are limited in speed and distance. Edge emitting lasers are fabricated in a chip and the laser is emitted from the edge of the chip. An edge emitting laser has a wavelength between 1300 mm and 1550 mm. An edge emitting laser may be used with a singlemode fiber. However, edge emitting lasers present problems in packaging.
FIG. 1 illustrates an example packaging of an edge emitting laser. The top edge of laser 110 has an anti-reflective (AR) coating while the bottom edge has a highly reflective (HR) coating. Light is generated and is emitted from the top edge, as shown in FIG. 1. The light is directed through lens 120. Residual light from the bottom edge of the laser is measured by photo detector 130. Feedback from the photo detector may be used to control the laser.
As seen in FIG. 1, the packaging of the edge emitting laser is a vertical packaging. This is a difficult process to implement because the laser must be aligned with the lens and the photo detector in a vertical orientation. Furthermore, due to the vertical orientation of an edge emitting laser, the process of aligning and packaging the laser cannot be fully automated. The manufacturer of the laser must either complete the assembly of the laser product or sell the laser chip itself. If a customer buys the laser chip without an assembly, the customer must then face the challenges of aligning, packaging, and testing the laser.
Therefore, it would be advantageous to provide a method and apparatus for packaging a laser in a planar orientation.